The input signal of a signal processing system, especially if this comes from magnetic transducers, mechanical transducers, tuners, etc., can be subject to large amplitude variations. Variations of 30-60 dB can occur under various circumstances. It is therefore useful to equip the system for processing the signal with a device for automatic gain control, commonly denoted by the acronym AGC, which determines a variable amplification of the input signal so as to obtain an amplified signal with constant amplitude at the output.
Some integrated circuit components have highly temperature-dependent intrinsic electrical characteristics. Notably, the junction V.sub.BE in silicon is inversely proportional to temperature, while the value of an integrated resistor is directly proportional to temperature.
In AGC systems and in analogous integrated circuits these variations in the electrical characteristics relative to the nominal design values, can often determine intolerable inaccuracies in the operation of these very sensitive circuits.